Resistance spot welding system and method

Abstract

A method and system for controlling a welding system collects material thickness data and material type data for a plurality of materials to be welded. A non-linear power profile is generated having a discrete stepped approximation of power over a period of time based on the material thickness data and the material type data to produce a desired current amount at a specific time during welding of the plurality of materials.

1 . A method for controlling a welding system comprising: 
 collecting material thickness data and material type data of a plurality of materials to be welded using the welding system;    generating a non-linear power profile having a discrete stepped approximation of power over a period of time based on the material thickness data and the material type data to produce a desired current at a specific time to weld the plurality of materials; and    using the desired current to form a weld nugget within the plurality of materials being welded.    
   
   
       2 . The method of  claim 1 , wherein generating the non-linear power profile comprises: 
 determining a desired power associated with the material thickness data and the material type data;    generating a desired power curve based on the desired power;    determining an amount of beginning power to be delivered at a beginning of a weld; and    reducing the amount of power over the period of time using a nonlinear rate of decay.    
   
   
       3 . The method of  claim 2 , wherein the desired power curve further includes having an optimal power characteristic.  
   
   
       4 . The method of  claim 2 , wherein the desired power curve further includes having an exponential decaying characteristic.  
   
   
       5 . The method of  claim 4 , wherein the exponential decaying characteristic is based on  
         p ( t )= P   0   e   −αt , 0 ≦t≦T  and    P   0   =αE /(1 −e   −αT )  
     where p(t) is the exponential decaying power characteristic, P 0  denotes power to be delivered at the beginning of the weld, at t=0, α is a time constant that controls a rate of decay of p(t), E denotes the desired amount of energy to be delivered to the weld nugget and T is a duration during which a weld current is applied.  
   
   
       6 . The method of  claim 1 , wherein the discrete stepped approximation is based on  
         p ( k )= p ( t   k ) where the stepped approximation includes N time segments having end points of which are denoted by time instances, t k ,1≦k≦N, and corresponding N power levels, p(k), 1≦k≦N.    
   
   
       7 . The method of  claim 1 , wherein producing the desired current amount further comprises: 
 sensing a welding current and a welding voltage;    estimating dynamic resistance of the materials based on the welding current and the welding voltage;    determining the desired current amount based on the dynamic resistance for the specific time.    
   
   
       8 . The method of  claim 7 , further comprising: determining a weld nugget size based on the dynamic resistance.  
   
   
       9 . The method of  claim 1 , further comprising: 
 determining a plurality of welding parameters to be used by the welding system based on the material thickness data and the material type data.    
   
   
       10 . The method of  claim 9 , wherein determining the plurality of welding parameters further comprises determining at least one welding parameter from an associated parameter look-up table.  
   
   
       11 . The method of  claim 9 , wherein determining the plurality of welding parameters further comprises retrieving at least one welding parameter from an associated parametric model.  
   
   
       12 . A resistance spot welding system comprising: 
 a user input device configured to allow a user to input material type data and material thickness data for a plurality of materials to be welded using;    a controller coupled to the user input device and operably generating a non-linear power profile over a period of time based on the material type data and the material thickness data to produce and transmit a desired current amount at a specific time to weld the plurality of materials; and    a pair of electrodes coupled to the controller and operably receiving the desired current to form a weld nugget within the plurality of materials being welded.    
   
   
       13 . The system of  claim 12 , wherein the non-linear power profile further comprises a discrete stepped approximation of power.  
   
   
       14 . The system of  claim 13 , wherein the discrete stepped approximation of power is based on  
         p ( k )= p ( t   k ) where the stepped approximation includes N time segments having end points of which are denoted by time instances, t k , 1≦k≦N, and corresponding N power levels, p(k), 1≦k≦N.    
   
   
       15 . The system of  claim 12 , wherein the controller is further configured to determine force, welding time and energy needed to weld the plurality of materials based on the material type and the welding material thickness.  
   
   
       16 . The system of  claim 12 , further comprising: 
 wherein the controller includes a plurality of sensors adapted to be coupled to the pair of electrodes for receipt of welding current and welding voltage, the controller determines dynamic resistance of the weld based on the welding current and the welding voltage and transmits a signal of the dynamic resistance;    a nugget prediction module coupled to the controller and configured to receive the signal, wherein the nugget prediction module estimates a nugget size based on a dynamic resistance signal and generates a nugget size signal;    an indicator coupled to the nugget prediction module and configured to receive the nugget size signal, wherein the indicator displays an estimated nugget size to an operator.    
   
   
       17 . The system of  claim 12 , wherein the desired nonlinear power curve further comprises an optimal power characteristic.  
   
   
       18 . The system of  claim 12 , wherein the desired non-linear power curve further comprises an exponential decaying characteristic.  
   
   
       19 . The system of  claim 18 , wherein the exponential decaying characteristic is based on  
         p ( t )= P   0   e   −αt , 0≦ t≦T  and    P   0   =αE /(1 −e   −αT )  
     where p(t) is the exponential decaying power characteristic, P 0  denotes power to be delivered at a beginning of the weld, at t=0, a is a time constant that controls a rate of decay of p(t), E denotes the desired amount of energy to be delivered to the weld nugget and T is a duration during which a weld current is applied.  
   
   
       20 . The system of  claim 12 , wherein the controller determines an amount of power to be delivered at a beginning of a weld and decreases power over the period of time.